Delay enable circuit

ABSTRACT

A delay enable circuit forming a means for pulsing a highvoltage power supply for a vacuum tube circuit until the cathode is sufficiently heated to allow the tube to function properly. When this proper functioning occurs, the enable circuit senses this fact and holds the high voltage on. The delay enable circuit also provides a means for applying an increased heater voltage to the tube during the warmup period, and cutting this voltage back to normal when the tube functions properly. This increased filament voltage provides a shorter warmup time without otherwise affecting the tube operation.

United States Patent 1 3,568,004

[72] lnventor Stephen D. Parker 2,526,421 10/1950 Riggs 317/22 Richmond, Ind. 2,539,208 1/1951 Schultz 328/270X [21] AppLNo. 868,539 2,971,137 2/1961 Stewart,Jr..... 317/142 [22] Filed Oct. 22, 1969 3,392,309 7/1968 Hickman 328/270X [45] Patented Mar. 2, 1971 [73] Assignee The United States of America as represented by the Secretary of the Navy Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorneys-R. S. Sciascia and Thomas 0. Watson, Jr.

[54] 'DELAY ENABLE CIRCUIT achims'lnnwmg Fig. ABSTRACT: A delay enable circuit forming a means for 1 [52] US. Cl. 317/141, pulsing a highwoltage power supply f a vacuum tube circuit 315/102, 317/146, 328/8, 328/270 until the cathode is sufficiently heated to allow the tube to [51] Int. Cl H02h 7/2 function properly. When this proper functioning occurs, the enable circuit senses fact and holds the voltage on 315/94, 102; 330/199, 201; 317/141, 146, 148.5 The delay enable circuit also provides a means for applying an increased heater voltage to the tube during the warmup [56] References Cited period, and cutting this voltage back to normal when the tube UNITED STATES PATENTS functions properly. This increased filament voltage provides a 2,052,725 9/1936 Roberts 328/270 shorter warmup time without otherwise affecting the tube 2,457,112 12/1948 Abercrombie et a1. 315/102X operation.

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nuaL: swrrcu LINES DELAY ENABLE CIRCIJIT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a delay enable circuit and more specifically to an enable circuit which delays the application of high voltage to a vacuum tube circuit until the cathode is sufficiently heated to allow the tube to function properly. 7

Certain types of RF circuitry employing vacuum tubes, such as oscillators and power amplifiers, cannot tolerate the simultaneous application of heater (filament) and anode'(plate) voltages. Expressed in other terms, the application of anode voltage must be delayed until the heaters have had an opportunity to raise the temperature of the cathodes to a level which will ensure that an adequate electronic emission is available.

An example of this type of circuit would be a high-power vacuum tube oscillator. If the anode voltage is applied before the cathode electron emission is able to support oscillation, then heavy DC plate currents will result.

The power dissipated during the warmup period, until the tube is able to oscillate, may be many times the normal operational average power and may exceed the dissipation ratings of both the oscillator tube aswell as the high-voltage power supply components. Preheating the cathodes with the anode voltage disabled will overcome this difficulty and oscillations will commence immediately when B voltage is supplied to the anode circuit.

2. Description of the Prior Art Prior'art protective devices to protect an RF circuit from damage often utilized a time delay when the heater supply was turned on, and at the end of the time-delay the high-voltage anode power supply would be enabled. The time delay period would be of adequate duration to insure that the cathode was brought up to the desired temperature level. However, the reliability of a time delay of this type is questionable, and in spite of accurate computations there could still be unforeseeable variables which would make the time delay inadequate thereby resulting in damage to the circuitry.

SUMMARY OF THE INVENTION The present invention overcomes the above enumerated shortcomings in the prior art devices and provides a delay enable circuit to sense the operational condition of the circuitry and take whatever action is required to protect the circuitry from damage, and to place the circuit in operation as quickly as possible. As a further improvement over the prior art the present invention, if the vacuum tube is not functioning correctly when anode voltage is applied, then the invention will (a) disable the anode power supply, (b) increase the heater voltage, (c) wait for a preselected time interval, reduce the heater voltage and reapply the anode voltage, (d) repeat the above cycle until correct operation is attained. The higher filament voltage significantly decreases the time required for heating. Furthermore, the ratio of the enable to disable time is apportioned in such a manner as to keep the dissipation of the tube and power supply components within tolerable limits. The delay enable circuit will sense when the tube circuit functions properly and the anode voltage connection is then con nected permanently. The delay enable circuit incorporates a double-pole two-position relay which performs the following functions:

I. The relay nonoperating.

a. A filament potential of l 1 volts is applied to the heaters. b. The anode supply voltage is disabled.

II. The relay operating.

a. A filament potential of 6.3 volts is applied to the heaters. b. The anode supply is enabled.

From the above discussion it is clear that the present inven-- tion offers a number of improvements over similar prior art devices. The invention offers a reliable, accurate and fast-acting safety device to protect high voltage RF circuitry from damage through the inadvertent and premature application of plate voltages to the tube.

An object of the present invention is the provision of a delay enable circuit.

Another object of the present invention is the provision of a delay enable circuit to protect high voltage RF circuitry.

Another object of the present invention is the provision of an enable circuit which senses the operational condition of the RF system.

Still another object of the present invention is the provision of a delay enable circuit which applies a higher than normal voltage to the heaters to shorten the cathode heating time.

Yet another object of the present invention is the provision of a delay circuit which senses when the tube circuit functions properly, whereupon it applies the anode voltage.

Other objects, advantages and novel features of the invention will become apparent from the following detailed descrip tion of the invention when considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a schematic diagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing there is shown a potential input terminal 10 which is connected to an off-on switch 12, this switch in turn being connected to 'a bus bar 14. Bus bar 14 is sectionalized by the silicon diode 23. Connected to bus bar 14 through resistors 20 and 22 are two NPN transistors 16 and 18 respectfully, the transistors being connected to form an astable multivibrator circuit. Transistor 16 has its collector cross-connected to the base of transistor 18 by means of a condenser 24, condenser 24 being connected by means of a resistor 16 to bus bar 14. The other half of the multivibrator, transistor 18, has its collector cross-connected to the base of transistor 16 by a condenser 28, this condenser being connected to bus bar 14 by means of a series resistor 30. A silicon diode 32 connects the emitter of transistor 16 to ground, the diode being poled so that its cathode is grounded. The emitter of transistor 18 is connected to ground by means of a resistor 34.

Also connected to the emitter oftransistor 18 is the base element of another transistor 36. The emitter of this component is connected to ground by means of a diode 38. The collector of transistor 36 is connected to a resistor 40, this resistor in turn being connected to bus bar 14 through a parallel circuit arrangement consisting of adiode 44 and a two position contact relay 42. One set of contacts for relay 42 is shown as a two-position switch 4648 while the other contacts of the relay are shown as a two-position switch 5052.

A fourth NPN transistor is shown as 54, this transistor having its collector connected to the bus bar 14 by a resistor 56, and its base connected to a parallel combination of two Zener diodes 58 and 60. Zener diode 58 has its cathode connected to the base of transistor 54 and its anode connected to ground, while Zener diode 60 has its cathode tied to the base of transistor 54 and its anode connected to terminal 52 of relay 42. A resistor 62 connects the base of transistor 54 to bus bar terminal 14. Contact 50 of relay 42 is connected by means of series resistor 64 to a firing terminal 66.

Returning now to the multivibrator circuit there can be seen that there is connected to the base of transistor 16 a series circuit consisting of a silicon diode 68, a Zener diode and a resistor 72. Diode 68 and Zener diode 70 are connected back to back with their cathodes tied together and this junction in turn is tied to ground by another diode 76 having its anode grounded. A capacitor 78 connects the junction of Zener diode 70 and resistor 72 to ground. One end of resistor 72 is connected as an input to RF circuitry 74 which is being protected from overload and which is shown generally within dotted lines. The heater circuit in RF circuitry 74 is connected to lead 80, this lead in turn being connected to the emitter of transistor 54.

A DC/DC converter 82 receives its potential input from a lead 84' connected to positive bus bar 14. The output from converter 82'is applied via a lead 86 to RF circuitry 74. Two other input leads to DC converter 82 appear as leads 88 and 90-, lead 88 being connected to contact 48 and lead 90 being connected to contact 46 of relay 42 respectively. A second off-on switch 92 is connected to potential bus bar 14 from potential input terminal94, this switch 92 being able to also apply 28 to 32 volts DC to the bus bar 14 as will be described hereinafter. i I

Turning now to the operation of the'device it will be seen that the delay enable circuit incorporates a double pole double position relay 42 which performs the following functions: (1) the relay nonoperating, the filament voltage on RF circuitry 74 is 11 volts and the anode supply is disabled. (2) With the relay 42 operating, the filament voltageis 6.3 volts and the anode supply is enabled; i

The filament voltage is adjusted by changing the base voltage of transistor 54' by shuntinga higher voltage Zener diode 58 with a lower voltage Zener diode 60 so that the normalaction of transistor 54 will control the heater voltage accordingly to RFcircuitry 74.

The DCIDC converter 82 may be of well-known transistorized type and the converter may be disabled by interrupting the base drive circuit by means of relay 42 shunting the starting bias current to ground through relay contacts 46. Conversely, the DC/DC converter is enabled by completing the base drive circuit through contact 48 and reapplying the starting bias current. Relay 42 is energized'primarily'by the operations of the multivibrator consisting of transistors 16 and 18 the operation ofwhich is as follows.

When the filament voltage is applied by means of switch 92 without applying the enable voltage (through switch 12) the relay coil 42 is energized and a 6.3 volt heater voltage will heatthe cathode of RF circuitry 74. However, the absence of enable voltage will preclude the application of anode voltage to the circuitry. The rel'aycoil 42 is-energized because the base of transistor 18 is biased forwardly through resistor 26, while transistor 16 is inactive. The resulting positive voltage across resistor 34 biases transistor 36 forwardly and the resulting col- I lector voltage energizes relay 42 through resistor 40.

The switch 92 is not closed and therefore the filament voltage is not applied while the enable switch 12 is closed and enable voltage is supplied then the astable multivibrator comprising transistors 16 and 18 will proceed to oscillate with a frequency of 4 cycles per second or a period of 250 milliseconds. The nonsymrnetry of the multivibrator will result since transistor 16 draws current for 230 milliseconds. For the reasons stated above whenever the transistor 18 draws current the relay coil 42 is energized. The relay selected for this purpose has a resonant frequency which is high enough to permit the relay to follow the operation of the multivibrator comprising transistors 16 and 18. Accordingly the voltages on the controlled stage 74 will be that the filament voltage will be nominal for 20 milliseconds and above nominal for 230 milliseconds while at the same time the anode voltage will be i nominal for 20 milliseconds 'and zero for 230 milliseconds. it

may be pointed out here that the application of filament voltage cannot generate oscillations in the multivibrator due to y the directivity of diode 23 connected in bus bar 14.

base of the transistor 16 from 1.2 volts to approximately zero.

A negative voltage of sufficient magnitude will therefore stop the multivibrator and render transistor 16 nonconductin Conversely, transistor 18 will conduct continuously and re ay coil 42 will be permanently energized, that 15 the RF power stage of circuitry 74 is supplied with nominal heater and anode voltages and the circuitry is operating normally. However, the power tube may be heated to an inadequate degree either by failure of thefilament supply or because insufficient time has beenallowed for the cathode to become heated. In that case insufficient voltage across the capacitor 78 is available and the application of enable voltage will cause the multivibrator to oscillate, which will increase the heater voltage to provide fast heating. It will also limit each try to energize the RF power stage to 20 milliseconds, and will continue trying every 250 milliseconds until success is achieved.

The diode 44 is used to dampen' transients resulting from stoppage of the current through relay coil 42.

The relay may also perform other functions such as removing a short circuit across a firing capacitor connected to terminal 66, through the operation of terminals 50 and 52 of the relay. I

From the above description of the structure and operation of the present invention it is obvious that the device offers considerably improvement over past protective circuits. The delay enable circuit which comprisesthe present invention provides a means for protecting a vacuum tube circuit until the cathode is sufficiently heated to allow the tube to function properly, and in accomplishing this end provides a means for applying an increased heater voltage to the tube during the warmup period, and cutting this voltage back to normal when the tube functions properly, at the same time permanently applying the high' voltage to the anode of the tube.

'Obviously, many modifications and variations of the present invention are possible in light of the above teaching.

' I claim:

1. A delay enable circuit for protecting a vacuum tube from damage until its cathode is sufficiently heated comprising:

' means for applying potential to the circuit;

means for applying increased filament potential to the vacuum tube during a warmup period;

means for sensing the operation of the tube being protected;

means responsive to the sensing means for removing the increased filament volta'ge to the tube and for applying anode voltage; and

control means for operating the sensing means.

2. The device of claim 1 wherein the means for applying potential to the circuit is a switch.

3. The device of claim 2 wherein the 'means for applying increased filament potential to the tube is a transistor with parallel-connected Zener diodes in its base circuit, one of said diodes having a lower voltage than the other.

4. The device of claim 3 wherein the sensing means is an astable multivibrator.

5. The device of claim 4 wherein one stage of the multivibrator conducts materially longer than the other, the increased filament potential being applied during the longer period.

6. The device of claim 5 wherein the responsive means is a two-position, double-contact, relay.

7. The device of claim 6 wherein one set of contacts on the relay connects into the circuit the said lower voltage Zener diode and the other set of contacts applies anode voltage to the tube.

8. The device of claim 7 wherein the control means cuts off the sensing means and leaves the anode potential connected to the tube being protected when said tube begins to conduct. 

1. A delay enable circuit for protecting a vacuum tube from damage until its cathode is sufficiently heated comprising: means for applying potential to the circuit; means for applying increased filament potential to the vacuum tube during a warmup period; means for sensing the operation of the tube being protected; means responsive to the sensing means for removing the increased filament voltage to the tube and for applying anode voltage; and control means for operating the sensing means.
 2. The device of claim 1 wherein the means for applying potential to the circuit is a switch.
 3. The device of claim 2 wherein the means for applying increased filament potential to the tuBe is a transistor with parallel-connected Zener diodes in its base circuit, one of said diodes having a lower voltage than the other.
 4. The device of claim 3 wherein the sensing means is an astable multivibrator.
 5. The device of claim 4 wherein one stage of the multivibrator conducts materially longer than the other, the increased filament potential being applied during the longer period.
 6. The device of claim 5 wherein the responsive means is a two-position, double-contact, relay.
 7. The device of claim 6 wherein one set of contacts on the relay connects into the circuit the said lower voltage Zener diode and the other set of contacts applies anode voltage to the tube.
 8. The device of claim 7 wherein the control means cuts off the sensing means and leaves the anode potential connected to the tube being protected when said tube begins to conduct. 